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  <div class="section" id="context-variables-objects">
<span id="contextvarsobjects"></span><h1>Context Variables Objects<a class="headerlink" href="#context-variables-objects" title="Permalink to this headline">¶</a></h1>
<div class="versionchanged" id="contextvarsobjects-pointertype-change">
<div class="admonition note">
<p class="admonition-title">Note</p>
<span class="versionmodified changed">Changed in version 3.7.1: </span><p>In Python 3.7.1 the signatures of all context variables
C APIs were <strong>changed</strong> to use <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> pointers instead
of <a class="reference internal" href="#c.PyContext" title="PyContext"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContext</span></code></a>, <a class="reference internal" href="#c.PyContextVar" title="PyContextVar"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextVar</span></code></a>, and
<a class="reference internal" href="#c.PyContextToken" title="PyContextToken"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextToken</span></code></a>, e.g.:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="c1">// in 3.7.0:</span>
<span class="n">PyContext</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>

<span class="c1">// in 3.7.1+:</span>
<span class="n">PyObject</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
</pre></div>
</div>
<p>See <a class="reference external" href="https://bugs.python.org/issue34762">bpo-34762</a> for more details.</p>
</div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
<p>This section details the public C API for the <a class="reference internal" href="../library/contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> module.</p>
<dl class="type">
<dt id="c.PyContext">
<code class="sig-name descname">PyContext</code><a class="headerlink" href="#c.PyContext" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Context</span></code></a>
object.</p>
</dd></dl>

<dl class="type">
<dt id="c.PyContextVar">
<code class="sig-name descname">PyContextVar</code><a class="headerlink" href="#c.PyContextVar" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.ContextVar</span></code></a>
object.</p>
</dd></dl>

<dl class="type">
<dt id="c.PyContextToken">
<code class="sig-name descname">PyContextToken</code><a class="headerlink" href="#c.PyContextToken" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.Token" title="contextvars.Token"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Token</span></code></a> object.</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContext_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContext_Type</code><a class="headerlink" href="#c.PyContext_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context</em> type.</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContextVar_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextVar_Type</code><a class="headerlink" href="#c.PyContextVar_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context variable</em> type.</p>
</dd></dl>

<dl class="var">
<dt id="c.PyContextToken_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextToken_Type</code><a class="headerlink" href="#c.PyContextToken_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context variable token</em> type.</p>
</dd></dl>

<p>Type-check macros:</p>
<dl class="function">
<dt id="c.PyContext_CheckExact">
int <code class="sig-name descname">PyContext_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContext_Type" title="PyContext_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContext_Type</span></code></a>. <em>o</em> must not be
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.  This function always succeeds.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_CheckExact">
int <code class="sig-name descname">PyContextVar_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContextVar_Type" title="PyContextVar_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextVar_Type</span></code></a>. <em>o</em> must not be
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.  This function always succeeds.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextToken_CheckExact">
int <code class="sig-name descname">PyContextToken_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextToken_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContextToken_Type" title="PyContextToken_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextToken_Type</span></code></a>.
<em>o</em> must not be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.  This function always succeeds.</p>
</dd></dl>

<p>Context object management functions:</p>
<dl class="function">
<dt id="c.PyContext_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_New</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a new empty context object.  Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error
has occurred.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Copy">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_Copy</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Copy" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a shallow copy of the passed <em>ctx</em> context object.
Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_CopyCurrent">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_CopyCurrent</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CopyCurrent" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a shallow copy of the current thread context.
Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Enter">
int <code class="sig-name descname">PyContext_Enter</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Enter" title="Permalink to this definition">¶</a></dt>
<dd><p>Set <em>ctx</em> as the current context for the current thread.
Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_Exit">
int <code class="sig-name descname">PyContext_Exit</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Exit" title="Permalink to this definition">¶</a></dt>
<dd><p>Deactivate the <em>ctx</em> context and restore the previous context as the
current context for the current thread.  Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success,
and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContext_ClearFreeList">
int <code class="sig-name descname">PyContext_ClearFreeList</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_ClearFreeList" title="Permalink to this definition">¶</a></dt>
<dd><p>Clear the context variable free list. Return the total number of
freed items.  This function always succeeds.</p>
</dd></dl>

<p>Context variable functions:</p>
<dl class="function">
<dt id="c.PyContextVar_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_New</code><span class="sig-paren">(</span>const char<em> *name</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *def</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a new <code class="docutils literal notranslate"><span class="pre">ContextVar</span></code> object.  The <em>name</em> parameter is used
for introspection and debug purposes.  The <em>def</em> parameter specifies
a default value for the context variable, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> for no default.
If an error has occurred, this function returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Get">
int <code class="sig-name descname">PyContextVar_Get</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *default_value</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> **value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Get" title="Permalink to this definition">¶</a></dt>
<dd><p>Get the value of a context variable.  Returns <code class="docutils literal notranslate"><span class="pre">-1</span></code> if an error has
occurred during lookup, and <code class="docutils literal notranslate"><span class="pre">0</span></code> if no error occurred, whether or not
a value was found.</p>
<p>If the context variable was found, <em>value</em> will be a pointer to it.
If the context variable was <em>not</em> found, <em>value</em> will point to:</p>
<ul class="simple">
<li><p><em>default_value</em>, if not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>;</p></li>
<li><p>the default value of <em>var</em>, if not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>;</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">NULL</span></code></p></li>
</ul>
<p>Except for <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the function returns a new reference.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Set">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_Set</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Set" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Set the value of <em>var</em> to <em>value</em> in the current context.  Returns
a new token object for this change, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyContextVar_Reset">
int <code class="sig-name descname">PyContextVar_Reset</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *token</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Reset" title="Permalink to this definition">¶</a></dt>
<dd><p>Reset the state of the <em>var</em> context variable to that it was in before
<a class="reference internal" href="#c.PyContextVar_Set" title="PyContextVar_Set"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyContextVar_Set()</span></code></a> that returned the <em>token</em> was called.
This function returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>

</div>


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